Eärendur succeeded his father Elendur on his death in T.A.777. Eärendur's rule was uneventful, but he was the tenth and last King of Arnor due to dissension amongst his sons.

After his death in 861, probably due to jealousy on the part of the two younger sons, his three sons split Arnor into three separate kingdoms: Arthedain, Cardolan and Rhudaur.

His eldest son and rightful heir, Amlaith of Fornost, became the first King of Arthedain, and it was through Amlaith and his heirs that the line of Isildur endured whilst the line of kings of Rhudaur and Cardolan failed - Aragorn II was a direct descendent of Amlaith, and it wasn't until Aragorn became king that Arnor was finally reunified.[3]

Eärendur is a Quenya name meaning "Servant of the Sea", and is a combination of the word ëar meaning "sea", and the suffix -ndur meaning "devotion to, friend of". It is unlikely that Eärendur himself was devoted to the sea: it is more likely that he was named after one of the two previous Eärendurs.